“Draft IEEE Standard for Local and metropolitan area networks, Part 16: Air Interface for Fixed and Mobile Broadband Wireless Access Systems Amendment for Physical and Medium Access Control Layers for Combined Fixed and Mobile Operation in Licensed Bands”, published on Sep. 18, 2004 will be referred herein as “IEEE 802.16 publication”. The disclosure of this reference is hereby incorporated herein by reference. The IEEE 802.16 publication is an international recommendation, which is being adopted for combined fixed and mobile operations. In an attempt to achieve efficient power utilization, a “sleep mode” procedure has been defined by that standard. This sleep mode procedure comprises virtually infinite sequence of listening windows (where the subscriber's terminal is ready to communicate with a base station) interleaved with sleep windows (where the terminal may power down so as to reduce the level of consumed power). According to this recommendation, the duration of each of the listening windows has a fixed size, while the duration of the sleep windows doubles in size, up to a certain limit. This procedure gives an adequate solution to cases where “random” traffic is conveyed, e.g. “bursty” IP traffic, like WEB browsing. Such traffic is typically characterized as being associated with non-real time MAC connections and best efforts type connections.
However, a problem arises when different types of services are rendered by a base station to a plurality of subscribers' terminals associated therewith, while the sleeping mode procedure is suitable for a single type of service having a random nature. Such a sleeping mode procedure cannot be adequately applied for services such as voice/VoIP applications on one hand and some other real time applications on the other, as the latter would typically have different patterns than the above-described ones, and consequently such a sleep mode procedure cannot be applicable for all these services.
Having to provide multicast/broadcast services to the different subscribers together with, say, having to provide WEB browsing services, would impose a problem as it will be virtually impossible to handle the different types of services while applying a single type of sleep mode procedure provided by the IEEE 802.16 publication.
Another problem arises in systems that support multicast services. Typically, the terminals are designed to have both multicast connections and unicast connections with different demand patterns, so that synchronization of sleep/listening cycles between different terminals would be nearly impossible. Under the IEEE 802.16 publication's sleep mode scheme, the only reasonable solution is to interrupt the sleep mode for all relevant terminals and to arrange for data transfer. The penalty associated with interrupting terminals in their sleep mode, is, that the interrupted terminal would be re-activated from the lowest value of the sleep window, which in turn causes a decrease in the efficiency of power saving.
Yet another problem that arises is when there is a need to combine the sleep mode operations with one or more management procedures like ranging, connections creation/configuration, SNMP etc. Suppose that a terminal is currently at a sleep mode as there is no traffic to be delivered via the existing connections and there is a need to add one more connection. In this case, the base station (“BS”) has to keep the terminal available for the corresponding transaction, although there is still no demand for using the existing connections, which means that there is in fact no reason to interrupt their sleep state. But in spite of the above, according to the procedure that has been commonly used in the art, the sleep mode of the terminal will be interrupted by “Traffic Indication” message (even though, as explained above, there is no traffic to be conveyed along the current connections), for applying the connection creation procedure. Consequently, the sleep mode procedure will have to be re-applied, from the lowest sleep window value.